I. Field of the Invention:
This invention relates to an improved auxiliary axle assembly for work vehicles and, in particular, for heavy load transporting vehicles such as ready-mix concrete trucks. More particularly, the improved tag axle assembly of the present invention is designed to attach to the rear end of the frame of a concrete truck so that the tires of the tag axle assembly can be lowered to ground engaging, truck supporting position or retracted to an elevated position so that the wheels straddle the sides of the truck frame above the ground where they will not engage obstacles in the truck's path as it traverses curbs, berms or other rough terrain at an off-road jobsite. Further, since the present invention is designed for use in connection with ready-mix concrete trucks, it incorporates features which permit the concrete delivery chutes of the truck to remain in their extended position irrespective of whether the tag axle assembly is in its raised or lowered position.
II. Discussion of the Prior Art:
In recent years there have been numerous efforts to develop improved tag axle assemblies attachable to heavy trucks so that such trucks can meet governmentally imposed weight restrictions. It has generally been the practice to design such tag axle assemblies so that the wheels can be placed in a ground engaging, truck supporting position while public roads are being traveled and capable of being elevated and stowed once the vehicle is about to leave the public road surface to better enable the truck to travel over rough, uneven and sometimes muddy or soft terrain at a jobsite. Thus, a very important element of any tag axle assembly design is the ability to easily and positively raise the assembly to a position where the assembly will have as much ground clearance as possible, yet maintain the lowest possible center of gravity. Persons skilled in the art have long recognized that there is a constant battle between the desire to elevate the tag axle assembly as high as possible to avoid obstructions yet not elevate the tag axle assembly so high that its weight significantly alters the center of gravity of the vehicle.
Various companies, including applicant's assignee, have patented or are attempting to patent devices to help vehicles meet load limit restrictions. McNeilus Truck and Manufacturing, Inc., for example, is the licensee of U.S. Pat. No. 4,492,389 issued Jan. 8, 1985, and is the owner of U.S. Pat. Application Ser. No. 813,419 (co-pending), filed Nov. 26, 1985 and U.S. Patent Application Ser. No. 006,217 (now U.S. Pat. No. 4,705,133), filed Jan. 23, 1987. As will be made clear from a subsequent discussion of the preferred embodiment, the apparatus of the present invention is somewhat similar to the apparatus described in U.S. Pat. Application Ser. No. 813,419 as well as the apparatus described in U.S. Pat. Application Ser. No. 006,217. However, the present invention is a great improvement over the designs described in these two applications for a variety of reasons. First, the present invention is easier to build and less costly to maintain than the designs described in either of these earlier-filed applications. Second, the apparatus of the present invention provides greater ground clearance than the apparatus described in either of these two applications. Third, the apparatus of the present invention permits the discharge chute of the concrete mixer to be in its extended position when the wheel assembly is being moved from its lower road engaging position to its upper, stowed position or visa versa. Finally, the design of the present invention provides an improved linkage for moving a fender associated with each wheel of the tag wheel assembly as those wheels are moved between their road engaging position and their stowed position.